This invention relates to an imaging element containing a blocked photographically useful compound such as a developing agent.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog. Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a Research Disclosure (129 (1975) pp. 27-30), describes the quaternary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity.
Recent developments in blocking and switching chemistry have led to blocked developing agents, including p-phenylenediamines, that perform relatively well. In particular, compounds having xe2x80x9cxcex2-ketoesterxe2x80x9d type blocking groups (strictly, xcex2-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the xcex2-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development. The xcex2-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
In addition to the aforementioned U.S. Pat. No. 4,157,915, blocked developing agents involving xcex2-elimination reactions during unblocking have been disclosed in European Patent Application 393523 and kokais 57076453; 2131253; and 63123046, the latter specifically in the context of photothermographic elements.
The incorporation of blocked developers in photographic elements is typically carried out using colloidal gelatin dispersions of the blocked developers. These dispersions are prepared using means well known in the art, wherein the developer precursor is dissolved in a high vapor pressure organic solvent (for example, ethyl acetate), along with, in some cases, a low vapor pressure organic solvent (such as dibutylphthalate), and then emulsified with an aqueous surfactant and gelatin solution. After emulsification, usually done with a colloid mill, the high vapor pressure organic solvent is removed by evaporation or by washing, as is well known in the art. Alternatively, solid particle (ball-milled) dispersions can be prepared using means well known in the art, typically by shaking a suspension of the material with zirconia beads and a surfactant in water until sufficiently small particle size is produced.
There remains a need for blocked photographically useful compounds with good keeping properties, which at the same time exhibit good unblocking kinetics. With respect to developing agents, it is an object to obtain a film incorporating blocked developing agents that provide good dye-forming activity and which, at the same time, yield little or no increased fog and/or provide little or no decrease in Dmax after storage.
In one application of the invention, it is a further object to obtain blocked photographically useful agents for use in photothermographic color films. With respect to developing agents, there is a continuing need for photothermographic imaging elements that contain a developing agent in a form that is stable until development yet can rapidly and easily develop the imaging element once processing has been initiated by heating the element and/or by applying a processing solution, such as a solution of a base or acid or pure water, to the element. A completely dry or apparently dry process is most desirable. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, relatively speaking, anytime and anywhere silver-halide film development.
Similarly, there is a need for incorporating other photographically useful compounds into a photothermographic element such that they remain stable until processing and are then rapidly released. Such photographically useful compounds include couplers, dyes and dye precursors, electron transfer agents, development inhibitors, etc., as discussed more fully below. The blocking of other photographically useful compounds, besides developing agents, are disclosed in the prior art. For example, U.S. Pat. No. 5,283,162 to Kapp et al. and U.S. Pat. No. 4,546,073 to Bergthaller disclose blocked development inhibitors, and U.S. Pat. No. 4,248,962 to Lau discloses blocked couplers wherein the blocking group in turn comprises a photographically useful group.
This invention relates to a blocked compound that decomposes (i.e., unblocks) on thermal activation by a 1,2 elimination mechanism to release a photographically useful group (also referred to herein as a PUG). In a preferred embodiment, the photographically useful group is a developing agent.
In one embodiment, thermal activation preferably occurs at temperatures between about 100 and 180xc2x0 C. In another embodiment, thermal activation preferably occurs at temperatures between about 20 and 140xc2x0 C. in the presence of added acid, base and/or water.
The invention further relates to a light sensitive photographic element comprising a support and a blocked compound that decomposes on thermal activation by a 1,2 elimination mechanism to release a photographically useful group.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a blocked compound (for example, a blocked developer) that decomposes on thermal activation by a 1,2 elimination mechanism to release a photographically useful group to form a developed image, scanning said developed image to form a first electronic image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, digitizing said first electronic record to form a digital image, modifying said digital image to form a second electronic image representation, and storing, transmitting, printing or displaying said second electronic image representation.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a blocked compound that decomposes by a 1,2 elimination mechanism to release a photographically useful group on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
In a preferred embodiment, the photographic element comprises an imaging layer having in association therewith a compound of Structure I: 
wherein:
PUG is a photographically useful group;
LINK 1 and LINK 2 are linking groups;
TIME is a timing group;
1 is 0 or 1;
mis 0, 1, or 2;
n is 0 or 1;
1+nxe2x89xa70;
t is 1 or 2 and when t is 2, the two T groups can combine to form a ring;
Y is C, N, O or S;
X is a substituted or unsubstituted aryl group or an electron-withdrawing group or is a heteroaromatic group which optionally can form a ring with a T or R12 group;
W is independently selected from hydrogen, halogen, or a substituted or unsubstituted (referring to the following W groups) alkyl (preferably containing 1 to 6 carbon atoms), cycloalkyl (preferably containing 4 to 6 carbon atoms), aryl (such as phenyl or naphthyl) or heterocyclic group; w is 0 to 3 when Y is C; w is 0-2 when Y is N; and w is 0-1 when Y is O or S; wherein when w is 2 the two W groups can combine to form a ring, and when w is 3, two W groups can combine to form a ring or three W groups can combine to form an aryl group or a bicyclic substituent; and wherein W in combination with T or R12 can form a ring;
R12 is hydrogen, or a substituted or unsubstituted (referring to the following R12 groups) alkyl, cycloalkyl, aryl, or heterocyclic group or R12 can combine with W, Y, or T to form a ring, preferably a non-aromatic ring;
T is a monovalent electron withdrawing group, a divalent electron withdrawing group (capped by a C1 to C10 organic group), an aryl group substituted with one to seven electron withdrawing groups, or a substituted or unsubstituted heteroaromatic group; or when T is a divalent electron withdrawing group, an aryl group, or a heteroaromatic group, it can combine with Y, W or R12 to form a ring system;
a is 1 when X is monovalent and 1 or 2 when X is divalent; and
b is 0 when X is monovalent and 1 when X is divalent.
Preferably, X is a terminal inorganic electron withdrawing group, for example xe2x80x94CNor xe2x80x94NO2, when it is monovalent; or an oxidized carbon, sulfur, or phosphorus atom in which the carbon, sulfur or phosphorous atom is attached to the adjacent Y group in Structure I, for example xe2x80x94COxe2x80x94 or xe2x80x94SO2xe2x80x94,when it is divalent.
Preferably, T is an inorganic group such as halogen, xe2x80x94NO2, xe2x80x94CN, or a halogenated alkyl group, for example xe2x80x94CF3, when it is monovalent. When it is divalent, T is preferably an inorganic electron withdrawing group capped by R13 (or by R13 and R14), for example, xe2x80x94SO2R13, xe2x80x94OSO2R13, xe2x80x94NR14(SO2R13), xe2x80x94CO2R13, xe2x80x94COR13, xe2x80x94NR14(COR13), etc., wherein R13 and R14 are independently a substituted or unsubstituted alkyl, aryl, or heterocyclic group, preferably having 1 to 10 carbon atoms.
By the term inorganic is herein meant a group not containing carbon excepting carbonates, cyanides, and cyanates. The term heterocyclic is defined herein to include aromatic and non-aromatic rings containing at least one (preferably 1 to 3) heteroatoms in the ring. If the named groups for a symbol such as T in Structure I apparently overlap, the narrower named group is excluded from the broader named group solely to avoid any such apparent overlap. Thus, for example, heteroaromatic groups in the definition of T may be electron withdrawing in nature, but are not included under monovalent or divalent electron withdrawing groups as they are defined herein.
When referring to electron withdrawing groups, this can be indicated or estimated by the Hammett substituent constants ("sgr"p, "sgr"m), as described by L. P. Hammett in Physical Organic Chemisty (McGraw-Hill Book Co., NY, 1940), or by the Taft polar substituent constants ("sgr"I) as defined by R. W. Taft in Steric Effects in Organic Chemistry (Wiley and Sons, NY, 1956), and in other standard organic textbooks. The "sgr"p and "sgr"m parameters, which were used first to characterize the ability of benzene ring-substituents (in the para or meta position) to affect the electronic nature of a reaction site, were originally quantified by their effect on the pKa of benzoic acid. Subsequent work has extended and refined the original concept and data, and for the purposes of prediction and correlation, standard sets of "sgr"p and "sgr"m are widely available in the chemical literature, as for example in C. Hansch et al., J. Med. Chem., 17, 1207 (1973). For substituents attached to a tetrahedral carbon instead of aryl groups, the inductive substituent constant "sgr"I is herein used to characterize the electronic property. Preferably, an electron withdrawing group on an aryl ring has a "sgr"p or "sgr"m of greater than zero, more preferably greater than 0.05, most preferably greater than 0.1. The "sgr"p is used to define electron withdrawing groups on aryl groups when the substituent is neither para nor meta. Similarly, an electron withdrawing group on a tetrahedral carbon preferably has a "sgr"I of greater than zero, more preferably greater than 0.05, and most preferably greater than 0.1. In the event of a divalent group such asxe2x80x94SO2xe2x80x94, the "sgr"I is for the methyl substituted analogue such as xe2x80x94SO2CH3 ("sgr"I=0.59). When more than one electron withdrawing group is present, then the summation of the substituent constants is used to estimate or characterize the total effect of the substituents.
In a preferred embodiment of the invention, LINK 1 and LINK 2 are of Structure II: 
wherein
Xxe2x80x2 represents carbon or sulfur;
Yxe2x80x2 represents oxygen, sulfur or Nxe2x80x94R1, where R1, is substituted or unsubstituted alkyl or substituted or unsubstituted aryl;
p is 1 or 2;
Z represents carbon, oxygen or sulfur;
r is 0 or 1; with the proviso that when Xxe2x80x2 is carbon, both p and r are 1, when Xxe2x80x2 is sulfur, Yxe2x80x2 is oxygen, p is 2 and r is 0;
# denotes the bond to PUG (for LINK 1) or TIME (for LINK 2):
$ denotes the bond to TIME (for LINK 1) or T(t) substituted carbon (for LINK 2).